The turn on of the blinker lamps on inexpensive vehicles (particularly on small engine motor vehicles) is controlled by an electronic device implemented with a dedicated integrated circuit. In this way, the use of a micro-controller, which is excessively expensive, may be avoided.
Referring to FIG. 1, an electronic system 1 controlling the turn on and off of the lamps of the blinkers 5, 6 of a vehicle is illustrated. The electronic system 1 includes an electronic device 2, a supply capacitor C1, a switch 3 (implemented, for example, with MOSFET type transistor), a mechanical change-over switch 4, and two lamps 5, 6 included in the left and right blinkers respectively. The switch 3 is interposed between a battery voltage Vbatt and the mechanical change-over switch 4, and the supply capacitor C1 is connected between the electronic device 2 and the mechanical change-over switch 4. Each lamp 5, 6 has a terminal connected to a ground reference and another terminal connected to the change-over switch 4.
The mechanical change-over switch 4 has the function of connecting, alternatively, the switch 3 to the lamp of the left blinker 5, to the lamp of the right blinker 6, or to a high impedance reference indicated in the following with Z∞, as a function of the blinker's driving command generated by the vehicle driver. The term “high impedance reference Z∞” may be understood as an impedance value greater than 30 kΩ. For example, the mechanical change-over switch 4 is positioned adjacent the driving wheel of a motor vehicle or on the handlebars of a motorcycle, and it is controlled by the driver of the motor vehicle or motorcycle by a three-positions lever in the case of a motor vehicle or by a three-positions button in the case of a motorcycle.
The electronic device 2 generates a control signal S1ctrl having a periodic trend (for example, a square wave having high and low logical values) to drive the control terminal t1ctrl of the switch 3 and to intermittently turn on lamp 5 (or 6) of a blinker when the latter is actuated, so that the vehicle driver can signal the change of direction. The control signal S1ctrl has, for example, a frequency equal to 1.42 Hz, which corresponds to a period of 704 ms. Typically, the length of the high edge in a period of the control signal S1ctrl is equal to the one of the low edge, that is, it is equal to 352 ms (which is commonly known as “duty-cycle” equal to 50%).
In particular, the operation of the electronic system 1 may be described by the following:
the driver actuates the left blinker, and the mechanical change-over switch 4 performs the connection of the output terminal t1out of the switch 3 to the lamp 5: the electronic device 2 generates the control signal S1ctrl having a periodic trend which periodically closes the switch 3 and thus the lamp 5 is intermittently turned on;
the driver actuates the right blinker, and the mechanical change-over switch 4 performs the connection of the output terminal t1out of the switch 3 to the lamp 6: the electronic device 2 generates the control signal S1ctrl having the periodic trend which periodically closes the switch 3 and thus the lamp 6 is intermittently turned on;
the driver deactivates a blinker, and the mechanical change-over switch 4 performs the connection of the output terminal t1out of the switch 3 to the high impedance reference Z∞: the lamp 5 (or 6) is turned off, while the electronic device 2 continues to generate the control signal S1ctrl having the periodic trend for a short time interval (1 second, for example) for discharging the supply capacitor C1, and thereafter takes null values.
It may be possible to observe that the electronic device 2 does not have a direct connection to a ground reference voltage. In fact, the electronic device 1 is connected to a ground reference voltage only when the driver has actuated a blinker (that is, the lamp 5 or 6 is connected to the switch 3), and only at instants when the corresponding lamp 5 or 6 is turned off, because this is substantially equivalent to a short circuit (for example, it has a resistance value less than 1 Ohm, typically on the order of 100 milli-Ohms).
Instead, the electronic device 2 loses the electrical connection to the ground reference voltage at instants when the corresponding lamp 5 or 6 is turned on, because this has a resistance value of a few Ohms to a few tenths of Ohms (20Ω, for example). Therefore, it may be desirable necessary to use the supply capacitor C1 to allow the electronic device 2 to correctly generate the control signal S1ctrl when a lamp 5 or 6 is connected. The supply capacitor C1 is charged when the control signal S1ctrl has a low logic value (and thus the lamp 5 or 6 is connected, but it is turned off), while the supply capacitor C1 is discharged (because it supplies the electronic device 2) when the control signal S1ctrl has a high logic value (and thus the lamp 5 or 6 is connected and it is turned on).
It is observed that the electronic device 2 continues to generate the control signal S1ctrl with a periodic trend for a short time interval also after the blinker has been deactivated (that is, when it is no more desirable for the vehicle driver to signal the change of direction). Because the supply signal is present, the supply capacitor C1 continues to supply the electronic device 2 for a determined time interval as the supply capacitor C1 is discharged. When the supply capacitor C1 is discharged (typically, after 1 second), the control signal S1ctrl takes null values.
It may be particularly desirable to control the value of the delay between the instant when the vehicle driver activates a blinker to turn on the corresponding lamp signaling the change of direction, and the instant when the first pulse of the control signal S1ctrl is generated (i.e., the instant between the activation of the blinker and the first transition from the low to the high logic value of the control signal S1ctrl). This delay (in the following referred as “delay of the first pulse”) generally has to be sufficiently short because it corresponds to the delay at which the first turn on of the lamp occurs. The first turn on of the lamp should be timely because it indicates to the drivers of surrounding vehicles that the vehicle is changing direction. For example, the value of the delay of the first pulse should be less than 100 ms (See, for example, the Japanese standard JIS D).
It may also be particularly desirable to control the value of the length of the high edge of the first pulse (referred in the following as “length of the first pulse”). The value of this length should be sufficiently high to enable the human eye of the driver of an adjacent vehicle to perceive that a blinker has been activated. For example, the length of the first pulse should be greater than or equal to 200 ms (See again, for example, the standard JIS D).
The Applicant has observed that the electronic system 1 of the known approach can fail to fulfill the requirements of the maximum delay of the first pulse and/or of the minimum length of the first pulse in the case the vehicle driver activates a blinker, deactivates the blinker, and activates again a blinker (the same or another) in a time interval less than the time for discharging the supply capacitor C1. In fact, as previously indicated, the electronic device 2 continues to generate the control signal S1ctrl with a periodic trend for a certain time interval also when the blinker of the lamp 5 or 6 has been deactivated (that is, when it is no more desirable for the vehicle driver to signal the direction change), and because the supply signal is present, the supply capacitor C1 continues supplying the electronic device 2 for a time interval wherein the supply capacitor C1 is discharged. If a blinker (the same or another) is again activated before the supply capacitor C1 is discharged, the instant when the blinker is activated is asynchronous with respect to the control signal S1ctrl, which has again periodical oscillations. This may cause the requirements of the maximum delay of the first pulse and/or of the minimum length of the first pulse to fail to be fulfilled.
For example, it is assumed that the control signal S1ctrl is periodic with a period equal to 704 ms and a duty cycle of the 50%, that is, the high length of the pulses is equal to 352 ms. Under this assumption, the blinker may be activated when the pulse of the control signal S1ctrl (still present by way of the supply capacitor C1) has maintained the high logic value for 200 ms. In this case, the first pulse of the control signal S1ctrl continues to have the high logic value for a further 152 ms (because the total length of a pulse is equal to 352 ms) and thus the requirement that the length of the first pulse must be greater than or equal to 200 ms is not fulfilled.
Another example is one wherein the blinker is activated when the pulse of the control signal S1ctrl (still present by way of the supply capacitor C1) has just terminated to maintain the high logic value and has performed a transition to the low logic value. In this case, the control signal S1ctrl maintains the low logic value for about 352 ms, and after about 352 ms does it transition to the high logic value, thus failing to fulfill the requirement of the delay of the first pulse which must be less than 100 ms.
Therefore, it may be desirable to control the maximum value of the delay of the first pulse and the minimum value of the length of the first pulse so that it fulfills the requirements set by various standards, for example, without a direct connection of the electronic device 2 to a ground reference voltage.